1. Field of the Invention
This invention relates to a screw and relates particularly to a wood screw.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional wood screw 1 comprises a head 11, a shank 12 extending from the head 11 and a drilling portion 13 disposed on the shank 12, opposite to the head 11. The shank 12 has a plurality of threads 121 spirally disposed thereon. The head 11 includes a top surface 111, a conical bottom surface 112 extending downwards from the top surface 111 and a plurality of ribs 113 disposed at intervals on the conical bottom surface 112. Referring to FIG. 3, when a user directs the drilling portion 13 at a wooden board 2 and rotates the head 11 to bore a hole 21 in the wooden board 2. Then, the thread 121 keeps drilling the shank 12 into the hole 21 until the head 11 touches the wooden board 2 and the ribs 113 cut wood burrs attached to a peripheral edge of the hole 21. Thus, the drilling operation is completed.
Because the wooden board 2 is formed with resilient wooden fibers, those spaced apart ribs 113 can only lift up the fibrous burrs but cannot cut and scrape off all of the burrs left on the hole 21 effectively. Such burrs incur a protrusion and render the head 11 difficult to be flush with a surface of the board 2. Thus, the fastening effect of the screw 1 cannot go well. Further, the head 11 does not provide a proper space for receiving the burrs cut by the ribs 113. This may stick some burrs out from the head 11 after the screw 1 is screwed into the wooden board 2. Thus, the screw 1 cannot achieve a good fastening effect.